This invention is directed to a technique for aspirating and expelling sample fluids of a test material and, more particularly, to an apparatus including micro-pipettes which can be adjusted as to the amount of the sample accommodated therein.
Laboratory analysis apparatus includes equipment for processing fluids, such as blood, to be analyzed. The fluid is contained in a holder such as a test tube. Only a predetermined amount of the test material must be removed. Equipment exists for reaching the test material with a probe such as a micro-pipette ("pipette" hereafter). A pipette has a cylindrical body with a long nose of small diameter. A piston in the body is moved by a rod to aspirate fluid into it or expel fluid from it. The extent to which the piston moves determines the amount of fluid sampled.
A conventional technique for controlling the amount of fluid sampled couples the rod to a stepper motor. The rotation of the motor can be accurately controlled. Such rotation is translated into axial motion of the rod by a suitable motion conversion mechanism. A large number of such samples can be taken simultaneously by putting the pipettes on a rack. The rod of each pipette is also connected to a rack which is moved by a motor. As the rack moves, all the samples are taken simultaneously.
An approach such as that described just above has several disadvantages. A relatively sophisticated and, therefore, expensive motor must be used to precisely and adjustably vary the motion of the rod. Also, the control circuitry for setting and adjusting the motor rotation is also sophisticated and expensive. Individual adjustment of a pipette relative to the other pipettes on the rack is not possible. Individual setting of this sort requires a dedicated motor for each pipette.